Today's semiconductor manufacturers rely on automated test equipment for testing semiconductor devices prior to shipment to customers. These testers are sophisticated processor-based systems, programmable to perform numerous types of electronic device tests.
The testing of integrated circuits may occur at various stages during the manufacturing process, provided that the units being tested are at a stage of manufacture where they are capable of some form of electronic testing and of electrical connection to pins of the test equipment. The testing may be "front-end" testing, such as of slices of wafers from which die for semiconductor devices will be cut. Or, the testing may be "back-end" testing of completed or nearly completed devices. In either case, the group of units being tested, that is, a group of slices or devices, is referred to as a "lot". "Final-testing" is a back-end test that ensures that the completed devices meet quality specifications before shipment to customers. Depending on when the testing occurs, the testing may be of AC, DC, parametric, or dynamic electrical characteristics.
A problem with semiconductor test equipment is that it can drift out of specification during testing. For this reason, users of such equipment perform test verification to ensure that test equipment is operating properly.
One approach to verification is to first test a number of lots. Samples are then randomly taken from these lots and retested. The theory is that if the retest confirms that the samples are good, then the first test must have been correct. Another approach to verification is based on the assumption that a test of a particular lot of integrated circuits is correct if it is known that the test equipment was operating properly before and after the lot was tested. This approach is described in U.S. patent application Ser. No. 08/368,683, entitled "Method for Final Testing of Semiconductor Devices", assigned to Texas Instruments Incorporated.
The test equipment may be programmed to perform self-testing to verify equipment performance, a process referred to as "diagnostic testing". The diagnostic test can be defined and supplied by the vendor of the test equipment or it can be defined by the user of the equipment.